Electrostatic printing with a magnetic brush feed



Dec. 19, 1967 w. J. THOMPSON ELECTROSTATIC PRINTING WITH A MAGNETIC BRUSH FEED Filed Jan. 17, 1966 INVENTOR W/l L M M f/Mltli 7 HUMP-50 V RNEY United States Patent 3,353,594 ELECTROSTATKC PRINTING WITH A MAGNETIC BRUSH FEED William James Thompson, Trenton, N.J., assignor to American Can Company, New York, N.Y., a corporation of New Jersey Filed Jan. 17, 1966, Ser. No. 521,144 8 Claims. (Cl. 101-414) This invention relates to electrostatic printing and more particularly to a method and means for feeding a mixture of magnetic particles and particles of printing material to and into the electrostatic field which effects transfer of the printing particles to an article to be printed upon.

Representative of the area in the field of electrostatic printing where-in the present invention is applicable are the following US. patents: 3,081,698, issued to Clyde 0. Childress and Louis I. Kabell; 2,820,746, issued to George F. Keeleric; and 2,152,077, issued to Archibald F. Meston and Harry A. Wintermute. These patents show the utilization of an electrostatic field, established between an article backing element and a particle charging element so that the charged particles are transferred from the charging element through the electrostatic field to the surface of the article to be printed or coated upon. Meston et al shows the use of a stencil screen that moves with and close to the article as the latter moves across the electrostatic field.

The present invention is a novel method and means for .mixing particles of printing material with particles of magnetic material, delivering the mixture to a printing or image screen or stencil through which the printing particles pass and are electrostatically propelled to the surface to be printed, and recovering the magnetic particles and any excess of printing particles which did not pass through the screen.

An object of the invention is the provision of a method .and means for feeding a mixture of magnetic-and printing particles onto an applicator prior to application of the mixture to a printing station.

Another object of the invention is the provision of a roller applicator of relatively small diameter and a conveying roller of larger diameter, both so magnetized as to arrange the particles in a uniform configuration.

Still another object of the invention is the provision of an applicator roller and a conveyor roller so that particles carried by the conveyor roller readily transfer from the conveyor roller to the applicator roller as they approach closely to the latter.

Yet another object oft-he invention is the provision of multipole magnetization on a roller feed system to provide the roller or rollers with multiple magnetic fields of suitable arrangement and strength to produce a desired layer of particle mixture thereon prior to printing.

Other objects and advantages of the invention will be apparent as it becomes better understood from the following description which, when read in connection with the accompanying drawings, discloses a preferred embodiment of the invention.

Referring to the drawings:

FIG. 1 is a vertical, longitudinal sectional view through apparatus illustrative of the invention; and

FIG. 2 is an elevational view taken along line 2-2 in FIG. 1.

With reference to FIG. 1, a supply of a mixture 11 of powdered iron or other magnetic particles and toner, powdered ink or other printing particles, is housed in a bin 12 formed in a frame 13. While the ratio of toner to magnetic particles may vary, it is preferred that the mixture be about toner to iron by weight. The toner or printing particles are smaller than the iron particles, for reasons to be explained hereinafter.

A relatively large magnetic conveyor or carrying roller 15 is fixedly mounted on a shaft 16 journaled in suitable bearings formed in the frame 13. Immediately above roller 15, and closely spaced therefrom, a magnetic applicator roller 17 is mounted on a shaft 18 journaled in bearings 19 formed on the frame 13.

Both of the rollers 15, 17 are rotated clockwise (FIG. 1) by a geared power drive 21 acting through a chain belt 22. The chain belt 22 takes over sprockets 23, 24 which are fixed, respectively, to the shaft 16, 18 and which also take over a drive sprocket 26, an idler sprocket 27 and a sprocket 28.

Sprocket 28 is fixed to a shaft 31 suitably mounted for rotation in the frame 13 and carrying thereon a leveling worm or anger 32 spaced a predetermined distance from the conveyor roller 15. The worm substantially uniformly spreads or distributes the mixture 11 laterally over the surface of the rotating roller 15.

The rollers 15, 17 may be of steel or other suitable rigid material. Each roller carries a layer of magnetic rubber bonded to its cylindrical surface. The magnetic rubber layer 37 on applicator roller 17 is preferably of greater thickness than rubber layer 35 on the conveyor roller 15 so that the magnetic particles in the mixture 11 will transfer from the relatively weaker magnetic attraction of the rotating conveyor roller 15 to the stronger magnetic attraction of the applicator roller 17 as the particles 11 approach the latter. 7

Furthermoreflhe layers 35, 37 have a multipole magnetization on substantially equally spaced centers parallel to their respective roller axes. If desired, the plurality of magnets may be arranged on a bias or a helix fashion in relation to the roller axes. The arrangement of the magnets on the surface of the rollerslS, 17 may, however, be positioned in any appropriate relationship to each other to provide the necessary uniform degree of mixture feed, without departing from the scope of this invention.

For their protection, each of the layers of magnetic material is covered with a suitable coating or layer 38 of non-magnetic plastic material, such as Mylar.

The magnetic particles in the mixture ll are attracted to the surface of the conveyor roller 15 and arrange themselves thereon in a brush-like formation, carrying with them the smaller printing particles. The rotating auger spreads the mixture laterally, and the multipole magnetization of the layer 35 causes the brush-like formation to assume a series of substantially uniform undulations 41 on the surface of the roller 15. The degree of undulation may be controlled by the relationship of the individual magnets to each other in the multipole magnetization.

As the mixture in this undulating conformation approaches the applicator roller 17, it is drawn from the weaker magnetic attraction of the roller 15 to the stronger magnetic attraction of roller 17 where the particles again assume an undulating brush-like conformation. If desired, a doctor blade or other suitable leveler may be used in conjunction with the applicator roller 17 in order to decrease the degree of undulation and thus deliver a more uniform quantity of particles to the printing area 44.

The particles are brushed onto and form a flat against a printing scrwn or stencil 45 having a mesh fine enough to block the relatively large magnetic particles but which permits the finer printing particles to pass therethrough.

Although this magnetic brush feed system is described in conjunction with a screen electrostatic printing system disclosed in the Childress et al. patent, it may also be used with electrostatic printing systems wherein the toner is not passed through a screen into the electrostatic field, although provision would have to be made for separating the toner from the magnetic particles.

A conventional electrostatic field 46 of sufiicient intensity is generated in the gap between the applicator roller 17 and an article 47 to be printed. Preferably, the article is disposed close to, but spaced from, the opposite side of the screen 45, and moving in clockwise direction (FIG. 1). The toner particles pass through the screen 45 into the electrostatic field 46 and are propelled and adhere to the article 47.

Preferably, the screen may be moved to the left (FIG. 1), in synchronism with movement of the article 47, but in opposition to the movement of the applicator roller 17 and the mixture 11 thereon, during a printing operation.

Following the printing operation, the screen 45 is raised out of contact with the brush-like conformation of the mixture on the applicator, and is moved to the right (FIG. 1) to repeat the printing cycle.

The magnetic particles and any excess of toner printing particles remaining on the applicator roller 17 are removed therefrom by a doctor blade 49 and gravitate, directed by suitable chutes or batfies 51, to the interior of roller 15. Fixed to interior portions of the roller are a plurality of vanes 52 so arranged that, as they move with the roller, they mix and direct the particles transversely across the interior of the roller and into the bin 12. Of course, other suitable means or chutes could be used to direct the doctored particles into the bin 12.

Addition of toner printing particles to the mixture is of course made continuously or intermittently to retain the mixture at a desired ratio of toner printing to magnetic particles.

It is thought that the invention and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes may be made in the construction and arrangement of the parts without departing from the spirit and scope of the invention.

I claim:

1. An electrostatic printing apparatus, comprising:

a source of a mixture of magnetic particles and chargeable printing particles; magnetic roller conveyor means having a surface layer of magnetic rubber of predetermined thickness for feeding said mixture of said magnetic particles and chargeable printing particles from said source to the surface of a movable applicator roller, the lower portion of said conveyor means being immersed in said mixture; said movable applicator roller having a surface carrying a multipole magnetization, said multipole magnetization extending across the roller in a fixed linear re- 'lationship;

said multipole magnetization on said applicator surface having a magnetic field strength greater than the magnetic field strength of said magnetic conveyor means;

means for creating an electrostatic field across a gap between said applicator means and an article to be printed upon, whereby said magnetic particles and chargeable particles are built up in a brush-like layer across the surface of said roller applicator means and said chargeable printing particles are transferred across a gap from said mixture on the applicator means to said articles;

and means for receiving, agitating and returning any eXcess mixture to said source, through said conveyor means.

2. The apparatus as set forth in claim 1 wherein said 4- multipole magnetization is oriented along lines substantially parallel to the axis of said roller conveyor means.

3. The apparatus set forth in claim 1 wherein the surface layer of the applicator roller is of magnetic rubber of predetermined substantially uniform thickness.

4. The apparatus set forth in claim 1 wherein said magnetic conveyor means for feeding the mixture of particles is a conveyor roller having a surface carrying a multipole magnetization along lines substantially parallel to the axis of the roller.

5. The apparatus of claim 1 wherein the thickness of said layer of magnetic rubber is greater on said applicator roller than on said conveyor roller whereby the field strength of the applicator roller is greater than that of the conveyor roller.

6. The apparatus set forth in claim 1 wherein the diameter of said conveyor roller is larger than that of said applicator roller.

7. The apparatus of claim 1 wherein there is provided means adjacent said source and spaced a predetermined distance from the surface of said conveyor roller for distributing and leveling the mixture over the surface of the roller as the mixture is picked up from the source by the magnetic surface of the roller.

8. A powder ink feeding device for use in an electrostatic printing apparatus, comprising:

a source of a mixture of magnetic particles and chargeable printing particles;

magnetic conveyor means having surface multipole magnetization for feeding said mixture from said source to a movable applicator which then carried said mixture into a printing screen within an electrostatic printing field; multipole magnetization on the surface of said applicator, the magnetic field strength of said applicator magnetization being greater than the magnetic field strength of said conveyor means; means for removing an excess of said mixture from said applicator and for delivering it to the interior of said conveyor means; and means within said conveyor means and movable therewith for receiving, agitating and returning said excess mixture to said source.

References Cited UNITED STATES PATENTS 3,003,462 10/1961 Streich 118-637 3,0l5,305 1/1962 Hall et al 118637 3,064,622 11/1962 Thompson 118-637 3,081,698 3/1963 Childress ct al. 3,081,737 3/1963 Frantz et al. 118-637 3,098,765 7/1963 Keller et al 118637 3,133,833 5/1964 Giaimo 118-637 3,140,199 7/1964 York. 3,145,122 8/1964 Streich. 3,152,012 10/1964 Schaffert. 3,152,924 10/1964 Wanielista et al. 118637 3,202,092 8/1965 Childress. 3,233,586 2/1966 Cranskens et al. 118--637 3,283,703 11/1966 Childress et al. 101-ll4 3,285,167 11/1966 Childress et al. 101--114 3,306,193 1/1967 Rarey et a1 101-414 E. S. BURR, Examiner. 

1. AN ELECTROSTATIC PRINTING APPARATUS, COMPRISING: A SOURCE OF A MIXTURE OF MAGNETIC PARTICLES AND CHARGEABLE PRINTING PARTICLES; MAGNETIC ROLLER CONVEYOR MEANS HAVING A SURFACE LAYER OF MAGNETIC RUBBER OF PREDETERMINED THICKNESS FOR FEEDING SAID MIXTURE OF SAID MAGNETIC PARTICLES AND CHARGEABLE PRINTING PARTICLES FROM SAID SOURCE TO THE SURFACE OF A MOVABLE APPLICATOR ROLLER, THE LOWER PORTION OF SAID CONVEYOR MEANS BEING IMMERSED IN SAID MIXTURE; SAID MOVABLE APPLICATOR ROLLER HAVING A SURFACE CARRYING A MULTIPOLE MAGNETIZATION, SAID MULTIPOLE MAGNETIZATION EXTENDING ACROSS THE ROLLER IN A FIXED LINEAR RELATIONSHIP; SAID MULTIPOLE MAGNETIZATION ON SAID APPLICATOR SURFACE HAVING A MAGNETIC FIELD STRENGTH GREATER THAN THE MAGNETIC FIELD STRENGTH OF SAID MAGNETIC CONVEYOR MEANS; MEANS FOR CREATING AN ELECTROSTATIC FIELD ACROSS A GAP BETWEEN SAID APPLICATOR MEANS AND AN ARTICLE TO BE PRINTED UPON, WHEREBY SAID MAGNETIC PARTICLES AND CHARGEABLE PARTICLES ARE BUILT UP IN A BRUSH-LIKE LAYER ACROSS THE SURFACE OF SAID ROLLER APPLICATOR MEANS AND SAID CHARGEABLE PRINTING PARTICLES ARE TRANSFERRED ACROSS A GAP FROM SAID MIXTURE ON THE APPLICATOR MEANS TO SAID ARTICLES; AND MEANS FOR RECEIVING, AGITATING AND RETURNING ANY EXCESS MIXTURE TO SAID SOURCE, THROUGH SAID CONVEYOR MEANS. 